Evaluation of Sampling Methods for Measuring Exposure to Volatile Inorganic Acids in Workplace Air. Part 2: Sampling Capacity and Breakthrough Tests for Sodium Carbonate-Impregnated Filters

Abstract

In France, the MétroPol 009 method used to measure workplace exposure to inorganic acids, such as HF, HCl, and HNO3, consists of a closed-face cassette fitted with a prefilter to collect particles, and two sodium carbonate-impregnated filters to collect acid vapor. This method was compared with other European methods during the development of a three-part standard (ISO 21438) on the determination of inorganic acids in workplace air by ion chromatography. Results of this work, presented in a companion paper, led to a need to go deeper into the performance of the MétroPol 009 method regarding evaluation of the breakthrough of the acids, both alone and in mixtures, interference from particulate salts, the amount of sodium carbonate required to impregnate the sampling filter, the influence of sampler components, and so on. Results enabled improvements to be made to the sampling device with respect to the required amount of sodium carbonate to sample high HCl or HNO3 concentrations (500 μL of 5% Na2CO3 on each of two impregnated filters). In addition, a PVC-A filter used as a prefilter in a sampling device showed a propensity to retain HNO3 vapor so a PTFE filter was considered more suitable for use as a prefilter. Neither the material of the sampling cassette (polystyrene or polypropylene) nor the sampling flowrate (1 L/min or 2 L/min) influenced the performance of the sampling device, as a recovery of about 100% was achieved in all experiments for HNO3, HCl, and HF, as well as HNO3+HF and HNO3+HCl mixtures, over a wide range of concentrations. However, this work points to the possibility of interference between an acid and salts of other acids. For instance, interference can occur through interaction of HNO3 with chloride salts: the stronger the acid, the greater the interference. Methods based on impregnated filters are reliable for quantitative recovery of inorganic volatile acids in workplace atmosphere but are valuable only in the absence of interferents.

Innovative Monitoring of Atmospheric Gaseous Hydrogen Fluoride

“…The sampler has an entry nozzle of aluminium (diameter: 10 mm and length: 9 mm) and of the total length 7 mm is a polytetrafluoroethylene-sealed O-ring that protrudes out of the front of the filter holder. The sampler design indicated that it can be used for sampling the inhalable fraction of aerosol, for which 90% of the mass size distribution is below 20  μ m. Moreover, the backup Swinnex allowed 94% ± 8% (4 mg/m 3 ; sampling time: 480 min) HF retention, in accordance with that proposed by Demange et al, 2011 [29], OSHA methods n. 21 [30], and PV2024 [31]. Desorption with 1.0 mL of 0.5 M phosphate buffer (pH 6.8) allowed a 98% recovery of fluoride from MCE filters impregnated with sodium carbonate (mean recovery of the spiked sodium fluoride).…”

New NIOSH Methods for Sampling and Analysis of Airborne Inorganic Acids

“…(11) The method has been independently verified for all three acids, (12) in accordance with applicable performance criteria. (10) An interlaboratory study with 5 participants found negligible biases and good agreement for HCl and HNO 3 at concentrations between 0.6 and 8 mg/m 3 for HCl and 0.8 and 10 mg/m 3 for HNO 3 . (13) Expanded method uncertainty estimates found were U < 12% for HCl and HBr and U <14% for HNO 3 .…”

“…(8) Also, no breakthrough of gaseous HF was observed from impregnated filters for up to 5 mg fluoride. (9,10) The component of the coefficient of variation of the method that arises from analytical variability, determined from the analysis of spiked filters, was 2.4% to 5.6% for HF and 1.7% to 3.3% for fluorides. (8,9) No effect of relative humidity (RH 20–80%) was observed on recovery of particulate fluoride over the concentration range of 0.3 – 5 mg/m 3 .…”

“…In the course of method validation using sodium carbonate-impregnated quartz fiber filters, (10,11,12) the estimated method detection limit (MDL) was 0.003 mg/filter for all three acids; this corresponds to an airborne concentration of 0.0012 mg/m 3 for a 240-L air volume. The working range was found to be (at least) 0.01 to 2.0 mg/sample for a 240-liter air sample.…”